The present invention is directed to a display device for displaying bright images on a dark background. The device utilizes a liquid crystal cell which has the liquid crystal layer, that can be switched at zones between two optically different states such as an inoperative state and an operative state, enclosed between two carrier plates with a predetermined wall orientation and the device includes a light trap in the form of a body containing fluorescent particles which body is made of a material with a refractive index of more than 1 and is provided with light emergent or exit windows that are disposed behind each of the switchable zones of the liquid crystal layer in the direction of observation.
In U.S. patent application Ser. No. 747,035, which issued as U.S. Pat. No. 4,142,781 and includes the disclosure of a German patent application P No. 25 54 226, a display device of a liquid crystal cell in conjunction with a light trap having exit windows and containing fluorescent particles was disclosed. Since the fluorescent body traps instant ambient light by the fluorescent dispersion and subsequent total reflection and then conducts it for exit through the exit or emergent windows with an increased intensity, a device of this type gives a particularly strong display. In this device, the amplification of the brilliance is essentially due to the large ratio of the light collecting area of the plate-shaped fluorescent body to the area of the light emitting or exit windows.
If a liquid crystal cell is operated on the basis of the polarization effect, the liquid crystal layer is usually placed between two linear polarizers. However, since polarizers drastically reduce the intensity of the light passing through the cell by filtering out one oscillation plane and in addition by the inevitable absorption that occurs by the polarizer, it is desirable to avoid the use of polarizers if possible. In addition, apart from increasing problems with assembly and durability, the polarizers prevent full exploitation of the very improvements in contrast and enlargement of the reading angle, which improvements were made possible by the light trap which included the fluorescent body.